This invention relates to a process for the protection of engraved rolls and plates for flexographic printing, intaglio or printing, or coating, wherein a base member of metal, on the surface of which a gravure is produced mechanically, electromechanically, or by means of etching, in correspondence with a desired embossed pattern, is provided and wherein protective layers for increasing corrosion resistance of a metal or of a metal compound or a ceramic component are applied on the engraved surface of the base member in order to increase the wear resistance and corrosion resistance.
It has been known for a long time to coat articles of metal with a protective layer for increasing corrosion resistance, hardness, and wear resistance. In particular, metallic articles are provided with a metallic coating of, for example, nickel or chromium in most cases by electrodeposition or by chemical reduction. In accordance with this electroplating method, it is possible to obtain, with nickel and, respectively, chromium, wearproof surfaces on metallic substrates with Vickers hardnesses of up to about 950 HV for nickel and 1200 HV for chromium, respectively. Vickers hardness HV is measured by using a foursided diamond pyramide with tip angle 136.degree..
It is furthermore known to vapor-deposit layer of hard material in a vacuum process onto metallic or nonmetallic surfaces of components in order to render the components wearproof. In the CVD process--chemical vapor deposition--the metallic proportion must first be released by cracking from a gaseous starting material before the metal reacts with the gas. The CVD process requires high reaction temperatures of about 800.degree. to 1100.degree. C. In the PVD process--physical vapor deposition--the metallic vapor is produced directly and reacts on the surface of the article to be coated with the gas to form the desired wear-resistant layer. The PVD method makes it possible to deposit the hard materials for the wearproof layer at temperatures of between 200.degree. and 650.degree. C.
For example German DE 38 09 139 describes depositing a special interlayer with a maximum thickness up to 5 .mu.m consisting of palladium-nickel-alloy electrolytically on a metal base or a synthetic resin base with the aim of improving the adhesion of an outer surface layer and applying an outer surface layer onto this interlayer by PVD using-metallic borides, carbides, nitrides or the like.
A special area for manufacturing products with wearproof surfaces is represented by rolls, or plates equipped with gravures which are also utilized as embossing tools. Such engraved rolls and plates have been realized heretofore with wearproof surfaces of high hardness of above 1700 HV merely on the basis of ceramic base members wherein the gravure is worked into the surfaces of the ceramic base member with the aid of laser beams in correspondence with the desired embossing patter. However, the gravures on the ceramic base members are not 100% reproducible on account of the numerous parameters that must be considered when machining ceramic components, so that each engraved roll or plate, with an identical gravure master, will turn out slightly different.